In order to obtain maximum production from an oil well which has been producing fluid containing a high percentage of water, horizontal well bores extending transversely from the vertical well bore are sometimes drilled. Because they extend into oil-producing formations above the source of the water, oil production is increased.
The concept of horizontal well bores goes back many years. It had been theorized for some time that they would have a beneficial effect on oil wells whose production had fallen below an acceptable level. It has been only relatively recently, however, in the last ten years or so, that the technology needed to drill horizontal well bores has been developed. This has involved the use of computer controlled drilling operations employing gyroscopes to maintain the drilling heads at the proper angle. In general, the drill is caused to enter the surrounding formation at a shallow angle to the vertical bore and is moved along an arcuate path until it reaches a point which is approximately at the same level as the point of entry. Because the radius of the arc is large, the newly drilled transversely extending bore is referred to as a horizontal well bore because it extends in a generally horizontal direction. To cause the drill bit to enter the formation at the proper angle and at the desired point along the length of calculated to be that which will cause the drill, upon contacting the whipstock, to be directed toward the wall of the vertical well bore at the correct angle.
It is of course desirable to avoid drilling into any area or zone which will cause gas or water to flow into the horizontal bore. Therefore, if sufficient information about the location of gas zones or aquifers exists, and if the drilling operation is properly controlled, a horizontal well bore can be provided which will avoid such areas. Even if a gas zone or aquifer is accidentally or mistakenly penetrated during the drilling operation, as long as it is discovered prior to removing the drilling tool and beginning production the formation can be plugged at the proper location by known techniques. In either case subsequent oil production will not contain excessive amounts of gas or water.
If, on the other hand, a horizontal well bore is drilled and production is begun without knowledge of an intrusion zone that subsequently causes unacceptable amounts of gas or water to enter the horizontal well bore, steps have to be taken to close off the area of breakthrough. To plug the permeable formation by known means would result in the plugging composition lodging in the horizontal well bore. Because the drilling equipment once removed cannot normally be returned to its exact previous location, it is extremely difficult to drill out plugging material from the horizontal well bore. What is needed is a method of shutting off the breakthrough of gas or water without requiring subsequent drilling and without plugging the horizontal well bore.